WASHINGTON -- Among Mahmoud Ahmadinejad, Andrew Meyer and Lawrence Summers, the world has been treated recently to a carnival of free expression as our most treasured right was exercised on university campuses.

In New York Monday, the president of Iran -- a liar who denies the Holocaust, sponsors terror and abuses human rights -- spoke at Columbia University.

Ahmadinejad (A'jad for short) was mocked, booed, jeered and laughed at -- especially when he insisted there are no gays in Iran despite documented public hangings of homosexuals, including teenagers. But he got to speak.

Summers wasn't so lucky. In California, the former president of Harvard University did not get to speak at a University of California Board of Regents meeting after professors petitioned to withdraw his invitation.

Summers didn't hang anybody in public or stone any adulterers, as is still common in Iran. Summers' offense was more nuanced. He was insensitive.

A couple of years ago at a conference, Summers suggested that disparities in accomplishment and college tenure among men and women could be explained (possibly, maybe, but maybe not) by "availability of aptitude at the high end," as well as socialization, patterns of discrimination and, not least, the "high-powered job hypothesis" that more men than women opt for 80-hour workweeks.

Which was, alas, the fate of Andrew Meyer, the University of Florida student who was subdued by campus police during a Q&A with Sen. John Kerry. Meyer, who calls himself The Andrew Meyer on his Web site, was guilty of acute self-importance, as the definite article before his name suggests.

As video of the incident showed, Meyer persisted in asking a string of questions when told to stop, and made a noisy scene when police attempted to escort him from the room. Finally, after he was pinned on the ground by five or six police officers, he was Tasered.

Whether The Andrew Meyer was obnoxious is not in dispute, but if obnoxiousness were a Tasering offense, America's talk show hosts would be an alternative energy source.

So there you have it: Three individuals trying to exercise freedom of speech in three different university environments with three different results. The one with the greatest credibility was censored. The one whose regime restricts academic freedom and imposes censorship was given a forum. The one whose participation in the free speech experiment arguably counts the most -- the student -- was physically punished.

Unfortunately, Meyer is not a particularly sympathetic character. His record suggests that he is motivated more by fame than principle. Even so, from the other side of the world where freedom of speech is rare -- and where students are brutalized or killed for protesting their government -- the Taser incident must have seemed familiar. It was not our best moment.

What these events tell us is that freedom of expression is a messy business, not so neatly understood or exercised. Even as we want to export freedom, we continue to struggle with it ourselves -- not because we are weak or stupid, but because freedom is a burden. It always has been.

America has toiled more than two centuries now, trying to craft a system of free expression that respects both the individual and the larger community. When should your right to express yourself prevail over my right not to share your expression? That's the trick question and the answer requires more than magic. It requires maturity, responsibility and vigilance.

Summers should have been allowed to talk, because the marketplace of ideas has room for unpopular thoughts. So should The Kid With The Big Mouth, because America has a demonstrable tolerance for big mouths.

Strong arguments can be made both for and against Ahmadinejad's "right" to speak. A president who doesn't tolerate free speech in his own country has no legitimate claim to the pulpit, but an American university president has every right to invite him, to hear and question him, and to expose and laugh at his deceptions.

Most important, allowing all to speak is a reiteration of our hard-won understanding that speaking freely in the public square beats strapping on bombs in the marketplace every time. That's a lesson worth modeling.